__author__ = 'Vivienfanghua'
from math import *
critics={'Lisa Rose': {'Lady in the Water': 2.5, 'Snakes on a Plane': 3.5,
 'Just My Luck': 3.0, 'Superman Returns': 3.5, 'You, Me and Dupree': 2.5,
 'The Night Listener': 3.0},
'Gene Seymour': {'Lady in the Water': 3.0, 'Snakes on a Plane': 3.5,
 'Just My Luck': 1.5, 'Superman Returns': 5.0, 'The Night Listener': 3.0,
 'You, Me and Dupree': 3.5},
'Michael Phillips': {'Lady in the Water': 2.5, 'Snakes on a Plane': 3.0,
 'Superman Returns': 3.5, 'The Night Listener': 4.0},
'Claudia Puig': {'Snakes on a Plane': 3.5, 'Just My Luck': 3.0,
 'The Night Listener': 4.5, 'Superman Returns': 4.0,
 'You, Me and Dupree': 2.5},
'Mick LaSalle': {'Lady in the Water': 3.0, 'Snakes on a Plane': 4.0,
 'Just My Luck': 2.0, 'Superman Returns': 3.0, 'The Night Listener': 3.0,
 'You, Me and Dupree': 2.0},
'Jack Matthews': {'Lady in the Water': 3.0, 'Snakes on a Plane': 4.0,
 'The Night Listener': 3.0, 'Superman Returns': 5.0, 'You, Me and Dupree': 3.5},
'Toby': {'Snakes on a Plane':4.5,'You, Me and Dupree':1.0,'Superman Returns':4.0}}

def sim_distance(prefs,person1,person2):
    si={}
    for item in prefs[person1]:
        if item in prefs[person2]:
            si[item]=1
    if len(si)==0:return 0
    sum_of_squares=sum([pow(prefs[person1][item]-prefs[person2][item],2) for item in prefs[person1] if item in prefs[person2]])
    return 1/(1+sqrt(sum_of_squares))
def sim_pearson(prefs,p1,p2):
    si={}
    for item in prefs[p1]:
        if item in prefs[p2]:
            si[item]=1
    n=len(si)
    if len(si)==0:return 1
    sum1=sum([prefs[p1][x] for x in si])
    sum2=sum([prefs[p2][x] for x in si])
    sum1Sq=sum([prefs[p1][x]*prefs[p1][x] for x in si])
    sum2Sq=sum([prefs[p2][x]*prefs[p2][x] for x in si])
    pSum=sum([prefs[p1][i]*prefs[p2][i] for i in si])
    num=pSum-sum1*sum2/n
    den=sqrt((sum1Sq-sum1*sum1/n)*(sum2Sq-sum2*sum2/n))
    if den==0:return 0
    return num/den
def topMatches(prefs,person,n=5,function=sim_pearson):
    scores=[(function(prefs,person,other),other) for other in prefs if other!=person]
    scores.sort()
    scores.reverse()
    return scores[0:n]
def getRecommendations(prefs,person,function=sim_pearson):
   totals={}
   simSum={}
   for other in prefs:
       if other==person:continue
       sim=function(prefs,person,other)
       if sim<=0:continue
       for item in prefs[other]:
           if item not in prefs[person] or prefs[person][item]==0:
               totals.setdefault(item,0)
               totals[item]+=prefs[other][item]*sim
               simSum.setdefault(item,0)
               simSum[item]+=sim
   rankings=[(total/simSum[item],item) for item,total in totals.items()]
   rankings.sort()
   rankings.reverse()
   return rankings
def transformPref(prefs):
    result={}
    for person in prefs:
        for item in prefs[person]:
            result.setdefault(item,{})
            result[item][person]=prefs[person][item]
    return result
if __name__=="__main__":
    print str(getRecommendations(critics,'Toby'))